Microphone



Jan'. 22, 1946. c. E. FRASER 2,393,318

MICROPHONE Filed Jan. 23, 1945 /6 I I 101/0 I AMPLIFIER SpMKEE l I m. ,4 I ,4 way] i: g:

/3 J sou/v0 WAVE 70 000 SPEAKER 7'0 LOUD SPEAKER I N V E IN TOR. C/zarles E Easel" ATTORNH Patented 1946 Application January 23, 1945, Serial No. 574,181

6 Claims. (Cl. 179-1) (Granted under the act March 3, 1883, as amended April 30, 1928: 3'10 0. G. 757) This invention relates to an apparatus for converting sound vibrations into electrical variations, and more particularly to a microphone adapted to minimize the disturbing eiiects of undesired sound waves-and audioregeneration, or

'* feed-back.

Most particularly, it is an object of my present invention to provide an improved microphone which will respond more readily to desired than undesired sound vibrations. v

A further object of my presentinvention is to provide an improved microphone of the electroacoustic transducer type selective with' respect to sound waves originating at diflerent positions and distances relatively to the microphone.

Still another object of my present invention is to provide an improved microphone which will substantially convert into electrical impulses, only sound vibrations originatingin a predetermined localized reglon with respect to the microphone.

It is also an object of my present invention to provide a microphone employing a pair oi coninto which the announcer may plug-in or connect a portable microphone at any of the various stations distributed about the ship, or throughout the industrial plant. Under such conditions there are usually stray noises due to the operaare used the announcement may be rendered unintelligible due to the stray noises or rrom regenerative audio feed-back.

' In underwater'detection, particularly where conventional microphones are utilized aboard moving vesselsylocal sound vibrations generated by the machinery and propellers aboard the vessel on which such microphones are located are detrimental with respect to the distance and identities of sound vibrations emanated by re- I mote targets.

It is among the more particular objects otthis invention to provide a' microphone and system which will substantially overcome these disadvantages and reproduce to greater extent the desiredsounds.

These obiects, and such objects as will hereintion of machinery and from other sources, so that when microphones oi the conventional type after appear or be pointed out, -wi1l be t be understood from the following description of several embodiments thereof, when read in connection with the accompanying drawing, in which Figure 1 is a schematic diagram indicating an electrical system which may be employed.

Figured is a sectional view 017 two electrodynamic microphones and associated electrical connections.

Figure 3 is a schematic diagram indicating the electrical connections of the moving coil elements.

Figure 4 is a sectional view of one form of my improved microphone with the cover partially shown.

Figure 5 is a face view oi the plate diaphragm in reduced scale.

Figured is aface view of the ring diaphragm in reduced scale.

Figure 4 shows one form oi microphone embodying my invention wherein circular permanent magnet l is housed in casing l and provided with circular slots 2 and 2a. Plate diaphragm 4- (as shown in Figure 5) and ring diaphragm 5, (shown in Figure 6) are concentrically posiwaves onto diaphragm 4. Cap 8 is also provided with a series of apertures i2 whereby undesired sound waves may be impressed on ring diaphragm 5. Extension 8 is extended toward-diaphragm 4 andserves to prevent the desired vibrations from reaching ring diaphragm 5. It will be readily understood that undesired sound vibrations will be impressed upon diaphragms 4 and 5 as indicated by arrows II and "a.

In Figure 2 the action of the two diaphragms, previously reierred to in Figure 4, and the electrical circuit connections of the coils lnopposed polarity are shown. In this figure apertures II of Figure 4 are indicated as sound director Ila. In Figure 2 the operation of this microphone is more clearly indicated by showing the permanent magnets i and la, diaphragms 4 and to, and

coils t and la with associated sound directing devices It andfla. In this figure the circuit connections in reversed polarity to the serially connected coils 6 and 1a clearly indicate that when sound vibrations of equal magnitude and phase relationship are impressed simultaneously on diaphragms 4 and 5a. the current generated in coils 6 and la will balance in opposed polarity and substantially no current will therefore flow to the loud-speaker.

Figure 3 indicates the wiring diaphragm of serially connected coils 6 and- 1 (Figure 4) in opposed polarity relationship and their resulting cancellation action when set into vibration by sound waves of equal magnitude and phase as indicated by arrows l3 and l3a.

Figure 1 indicates one form of schematic wiring diagram embodying an amplifier H, a loudspeaker l5, and a series of jacks l6 into which conductor l8 to plug member I9, may be connected. This indicates the system usually used tion is to be utilized.

From the foregoing description it will be apparent to those skilled in the art that I have provided an improved microphone which is more sensitive to desired than undesired sound waves than are conventional microphones. Although, I have shown and described several embodiments centric slots in which said coils operate, means microphone l'l,. connected by means of flexible I for directing desired and undesired sound waves upon said diaphragms, and an electrical system whereby the currents generated in said coils by the action of said diaphragms due to undesired sound waves are substantially annulled.

3. In combination, a magnetic microphone having two concentric diaphragms each supporting a coil, a magnet provided with concentric shots in which said coils operate, means for directing desired and undesired sound waves upon said diaphragms, said coils being serially 'con-' nected in opposed polarity whereby the currents generated by the action of said diaphragms due to undesired sound waves are substantially annulled.

4. In a microphone, a pair of electroacoustic elements concentrically located, means for impressing desired sound waves on one of said elements, means for impressing undesired sound waves on both of said elements, and means for permitting the effects of the desired sound waves to predominate.

of my present invention, it will .be apparent to those skilled in the art that many other modifications thereof are also possible. For example, I may use microphone elements of the crystal, condenser, thermal, ribbon, or other suitable type with their required associated circuits. I therefore do not wish to be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

The invention described herein maybe manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

5. In a microphone, a pair of concentric diaphragms, means for impressing desired sound waves on one of said diaphragms, means for impressing undesired sound waves on both of said 40 diaphragms, and means for permitting the effects o! the desired sound waves to predominate.

6. Ina microphone, a pair of concentric diaphragms, means for impressing desired sound waves on one of said diaphragms, means for impressing undesired sound waves on both of said diaphragms, and means for substantially neutralizing the effects of the undesired sound waves whereby the effects of the desired sound waves predominate.

CHAS. E. FRASER. 

